1. Field of Invention
This invention relates to rotating machinery, specifically to rotating data storage devices such as hard disk drives, and particularly to achieving rotational start-up and power conservation in hard disk drives.
2. Discussion of Disk Drives
Present day, digital computing systems generally employ one or more data storage devices known as "disk drives" for non-volatile, random-access, mass storage of digital data. Disk drives incorporate rotating, data storage media in the form of disks or platters. These disks may be rigid or flexible. They may be coated with a magnetic emulsion for reading and writing in a fashion similar to that of magnetic recording tape, or they may be configured with a photo-sensitive layer such that data may be recorded and read by laser beam(s) in an optical data recording format. Other methods for recording on rotating media exist, and the rotating medium itself may take forms other than dusk, such as a drum. At this present time, however, disk-based media dominate the random-access, non-volatile, data mass storage field.
Three clear and driving trends exist in the disk drive marketplace at present: increasing speed, diminishing power consumption, and shrinking cost. The growing size and complexity of computer software programs drive the need for faster, more responsive disk drives in ever-smaller physical form factors. In addition, energy conservation is becoming increasingly important for battery life extension in the rapidly growing area of portable applications, as well as for environmental reasons.
In order to address the power conservation issue, disk drives are commonly placed into an idle or "sleep" mode after a pre-determined period of non-activity in order to conserve energy. In the sleep mode, only a skeletal amount of electronics remain active, and the spindle motor is de-energized, allowing the disk platter assembly to spin to a stop. When the host computing system again calls for access to disk data, the drive is re-awakened, re-energizing the electronics and the spindle motor. Unfortunately, the process of accelerating the platter assembly from a complete stop back to full operational speed has three significant drawbacks: (1) it consumes an significant amount of time (several seconds), which is in direct conflict with the desire for increased computer system speed; (2) it requires a momentary, extra large burst of energy to accelerate or "spin-up" the disks, which is in direct conflict with the desire to minimize power consumption; (3) the electrical current peak during start-up requires that both the disk drive spindle motor and the electronics which operate it be designed to handle these frequent, large, start-up surges, which conflicts with the desire to maintain low overall system cost.
It is clear, then, that a technique is needed which:
reduces the amount of time required to start or re-awaken a stopped or "sleeping" disk drive; PA1 minimizes the amount of electrical surge current required to start or re-awaken a stopped or "sleeping" disk drive; PA1 achieves this re-restart function cheaply, reliably, and with a minimum of complexity or additional components. PA1 Faster acceleration of a disk drive's platter assembly to its final rotational speed than is achievable with a spindle motor alone allowing data read/write operations to be made very quickly. PA1 Very simple, straightforward attainment of appropriate starting force direction, without any gearing or complex torque reversing mechanism. PA1 Recapture/conservation of otherwise wasted kinetic (rotational) energy at shut-down. PA1 No energy drain during normal operation, preserving battery life. PA1 Re-use of captured energy at start-up, preserving battery life. PA1 Allows the disk drive to be put to sleep after shorter pauses in computer host activity because it can be re-awakened more quickly. Since this further reduces the total amount of time the drive is awake, it conserves additional energy and further extends battery life. PA1 Reduction in peak-current and peak-torque requirements in the spindle motor and motor driver electronics, reducing their size and cost.